Wireless communication devices usually comprise transceivers which comprise receivers and transmitters. A frequency multiplier, together with a low frequency oscillator, is able to provide high purity and stable signal sources for a transceiver in a wireless communication device. The frequency multiplier multiplies an input signal with a low frequency fin, to an output signal with a desired high frequency fout, where fout=n*fin, and n is an integer multiplication factor. For example, a frequency tripler can convert an input signal frequency with fin to fout=3fin. A bandwidth of a frequency multiplier refers to a frequency range of the output signal. A broadband frequency multiplier can be applied in multi-band transceivers, as well as a high-resolution Frequency Modulated Continuous Wave (FMCW) radar. Up to now, a broadband frequency tripler is usually made up of two diodes, as shown in FIG. 1, achieving a wide 3-dB bandwidth from 80 GHz to 110 GHz. For example, in Gui-Yu Chen. et al., “A 60-110 GHz Low Conversion Loss Tripler in 0.15-um MHEMT Process”, IEEE Microwave Wireless Component Letter, 2016, in Tomas Bryllert et al., “A Broadband Heterostructure Barrier Varactor Tripler Source”, IEEE International Microwave Symposium (MTT-S), 2010, and in Tero Kiuru et al., “Compact Broadband MMIC Schottky Frequency Tripler for 75-140 GHz”, Proceedings of the 6th European Microwave Integrated Circuits Conference, pp 108-110, 2011, diode triplers are disclosed.
Unfortunately, a frequency tripler built by diodes has a large conversion loss, and requires a large input power. Typically, such kind of tripler has a conversion loss around 20 dB with an input power of 15 dBm. Therefore, it is necessary to have a power amplifier at the output and another power amplifier at the input, to boost the output/input power. Such kind of multiplier chain consumes a lot of Direct Current (DC) power.
On the other hand, a frequency tripler built by transistors has probably a positive conversion gain, driven by a relative low input power. For example, a D-band frequency tripler in M. Bao et al., “A high power-efficiency D-band frequency tripler MMIC with gain up to 7 dB,” IEEE Microwave Wireless Component Letter, vol. 24, no. 2, pp. 123-125, February 2014, has a conversion gain of 7 dB with an input power of 3 dBm. However, the transistor tripler has a narrow 3-dB frequency bandwidth of 16 GHz, i.e. from 119 GHz to 135 GHz.